gpu: ipu-di: Add ipu_di_adjust_videomode()

On some monitors, high resolution modes are not working, exhibiting
pixel column truncation problems (for example, 1280x1024 displays as
1280x1022).

The function ipu_di_adjust_videomode() aims to fix these issues by
adjusting a passed videomode to IPU restrictions. The function can
be called from the drm_crtc_helper_funcs->mode_fixup() methods.

Signed-off-by: Jiada Wang <jiada_wang@mentor.com>
Signed-off-by: Deepak Das <deepak_das@mentor.com>
Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>